DenverSpine - Spinal Anatomy

To communicate with your back doctor, it helps to know the terms your physician might use to explain and describe your condition. Just as dentists use a number to identify each tooth, a spine doctor has a labeling system for each link on the chain that makes up the spinal column. To clear things up a bit, here is a "crash course" in spinal anatomy.

Spinal column

When viewed from the side, a healthy spinal column is slightly S-shaped. The top seven vertebrae are known as the cervical vertebrae, labeled C1 through C7.

The chest area contains the thoracic vertebrae, T-1 through T-12. The thoracic vertebrae do not rotate as much as the neck and low back. Consequently, this area of the spine is more stable and is generally less susceptible to injury. Relatively few back pain cases involve the T-level vertebrae.

Below the thoracic vertebrae are the five lumbar vertebrae, and below that is the sacrum. The lumbar vertebrae are labeled L1 to L5. This area is the most prone to injury, because it bears the most weight when you sit, stand, push, pull or lift.

Below the lumbar spine area is a series of fused bones known as the sacrum. At the bottom tip of the spinal column structure is the coccyx or the tailbone.

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Each rounded vertebra body has pedicles and laminae, facet joints, and the bony transverse and spinous processes, which are the narrow, finger-like spikes pointing out from the sides and back of the vertebra.

This spinal column is held in place by surrounding muscles, ligaments and tendons that act as supporting guy wires. When working properly, the spine is able to bend and twist. When muscles and ligaments weaken, problems arise in the stability of the spine. Muscles and ligaments can strain, and discs and facet joints can be injured.
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Cervical spine

The cervical vertebrae make up the neck. Each vertebra in the cervical region is labeled C-1 through C-7. The cervical vertebrae protect the spinal cord, which attaches to the brain.
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The spinal cord

Within this column of vertebrae is the spinal cord, which travels from the brain stem down through the back. The spinal cord acts as our main electrical wiring system and is protected by the bony vertebrae. At every vertebrae level, there are nerve roots that branch off the spinal cord. When a disc herniates, it can crimp or pressure these nerve roots, which can cause excruciating pain that radiates into an arm or leg.

Nerve impingements in the cervical area can cause pain to radiate into the shoulder and arm. When discs are injured in the low back area, pain can radiate into the legs.
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Lumbar spine and sacrum

The lumbar area, or low back, contains L-1 through L-5, the largest, most sturdy group of vertebrae. Because it bears most of the body's weight when we sit, stand, push, pull, lift and move, the lumbar section is considered the most injury-prone area of the spine. The spinal cord threads from the brain down through the spine and ends at about L-2, where it forms a bundle of nerves known as the cauda equina (Latin for 'horse's tail'). From the neck area to the coccyx are 31 pairs of nerve roots that exit the spinal canal and head for remote areas of the body through vertebral portals called foramina. At the base of L-5 is a solid mass of five fused bones called the sacrum (pronounced 'say-crum'). Finally, the spinal column ends at the coccyx (pronounced 'cock-six'), or tailbone, which is actually several small bones fused together.
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Click on image to enlarge

Healthy Disc

The spinal disc is like a jelly doughnut. The "jelly" of the doughnut represents the "disc nucleus," and the material that encases the "jelly" is called the "disc annulus." The disc acts likes a rubber shock absorber between the vertebrae. The facet joints act as hinges that allow for twisting and turning of the spinal column. The spinal cord threads through from top to bottom like a telephone wire system.
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Muscles

The back muscles provide support for the spine, allowing us to comfortably carry out our everyday activities. Back muscles can be grouped into three main categories. First, the extensor muscles allow us to stand up straight. Secondly, the flexor muscles allow us to bend forward. Finally, the oblique muscles enable us to rotate from side to side and keep everything stable and aligned.

If you think of the spine as a tall radio tower that must withstand the force of crosswinds, the muscles and ligaments of the back are the guy wires that provide support to the tower. The extensor muscles enable us to arch our back and are located in the back. Flexor muscles are also known as abdominal (stomach) muscles and are located in front of the spine. The oblique muscles are located on our sides, around the waist area, and they help stabilize our torsos and control the pelvis.
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Joints

Facet joints are the main "hinges" in our backs, allowing the muscles and vertebrae to move properly. Joints can lose their lubrication, swell and become painful, but if "well-oiled" with exercise and gentle stretching, joints will remain healthy.
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Learn more about spinal anatomy through the North American Spine Society.

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